net.sf.saxon.expr.sort

## Class NumericComparer

- java.lang.Object
- - net.sf.saxon.expr.sort.NumericComparer

- All Implemented Interfaces:
    Serializable, AtomicComparer
  Direct Known Subclasses:
    NumericComparer11

      public class NumericComparer
      extends Object
      implements AtomicComparer, Serializable

  A Comparer used for comparing sort keys when data-type="number". The items to be compared are converted to numbers, and the numbers are then compared directly. NaN values compare equal to each other, and equal to an empty sequence, but less than anything else.

  This class is used in XSLT only, so there is no need to handle XQuery's "empty least" vs "empty greatest" options.
  Author:
    Michael H. Kay
  See Also:
    Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected StringToDouble` | `converter`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `NumericComparer()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `compareAtomicValues(AtomicValue a, AtomicValue b)` Compare two Items by converting them to numbers and comparing the numeric values.
    `boolean` | `comparesEqual(AtomicValue a, AtomicValue b)` Compare two AtomicValue objects for equality according to the rules for their data type.
    `StringCollator` | `getCollator()` Get the collation used by this AtomicComparer if any
    `ComparisonKey` | `getComparisonKey(AtomicValue a)` Get a comparison key for an object.
    `static NumericComparer` | `getInstance()`
    `AtomicComparer` | `provideContext(XPathContext context)` Supply the dynamic context in case this is needed for the comparison

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### converter

          protected StringToDouble converter

  - ### Constructor Detail

    - #### NumericComparer

          protected NumericComparer()

  - ### Method Detail

    - #### getInstance

          public static NumericComparer getInstance()

    - #### getCollator

          public StringCollator getCollator()

      Description copied from interface: `AtomicComparer`
      Get the collation used by this AtomicComparer if any
      Specified by:
        `getCollator` in interface `AtomicComparer`
      Returns:
        the collation used for comparing strings, or null if not applicable

    - #### provideContext

          public AtomicComparer provideContext(XPathContext context)

      Supply the dynamic context in case this is needed for the comparison
      Specified by:
        `provideContext` in interface `AtomicComparer`
      Parameters:
        `context` - the dynamic evaluation context
      Returns:
        either the original AtomicComparer, or a new AtomicComparer in which the context is known. The original AtomicComparer is not modified

    - #### compareAtomicValues

          public int compareAtomicValues(AtomicValue a,
                                AtomicValue b)

      Compare two Items by converting them to numbers and comparing the numeric values. If either value cannot be converted to a number, it is treated as NaN, and compares less that the other (two NaN values compare equal).
      Specified by:
        `compareAtomicValues` in interface `AtomicComparer`
      Parameters:
        `a` - the first Item to be compared.
        `b` - the second Item to be compared.
      Returns:
        <0 if a0 if a>b
      Throws:
        `ClassCastException` - if the objects are not Items

    - #### comparesEqual

          public boolean comparesEqual(AtomicValue a,
                              AtomicValue b)

      Compare two AtomicValue objects for equality according to the rules for their data type. UntypedAtomic values are compared by converting to the type of the other operand.
      Specified by:
        `comparesEqual` in interface `AtomicComparer`
      Parameters:
        `a` - the first object to be compared.
        `b` - the second object to be compared.
      Returns:
        true if the values are equal, false if not
      Throws:
        `ClassCastException` - if the objects are not comparable

    - #### getComparisonKey

          public ComparisonKey getComparisonKey(AtomicValue a)

      Get a comparison key for an object. This must satisfy the rule that if two objects are equal according to the XPath eq operator, then their comparison keys are equal according to the Java equals() method, and vice versa. There is no requirement that the comparison keys should reflect the ordering of the underlying objects.
      Specified by:
        `getComparisonKey` in interface `AtomicComparer`

Copyright (c) 2004-2013 Saxonica Limited. All rights reserved.